Vitreous and vitrdyiable composi



Patented Jan. 14, 1947 VITREOUS AND VITRIFIABLE COIlflOSI- TIONS OFMATTER AND METHODS OF MAKING THE SAME Harold R. Feichter, Canton, Ohio,assignor to United States Quarry Tile Company, Canton, Ohio, acorporation of Delaware N Drawing.

Original application August 27,

1942, Serial No. 456,414. Divided and this application May 27, 1946,Serial No. 672,690

The discovery and invention relate in general to compositions of matterfor vitreous products and the like, and for vitrifiable bodies and thelike, and methods of making the same.

The discovery and invention particularly relate to substances requiringhigh temperatures for vitrification, and more particularly tocompositions of matter including aluminum oxide, and this application isa division of my application, Serial No. 456,414, filed August 27, 1942.

Products made by vitrifying or firing at high temperatures, bodycompositions having as their principal constituent aluminum oxide areused as spark plug insulators, particularly for aircraft engines, wearresistant and similar parts having extreme hardness, and for otherpurposes.

Spark plug insulators adapted for use in a high compression internalcombustion engine such as an aircraft engine or motor becomeincreasingly difficult to produce, the higher the compression of theengine, and the tendency is always to increase the compression of anaircraft engine whenever possible.

Mica has been used for the insulators of aircraft engine spark plugs,but'most mica having the required special mineral and physicalproperties must be imported into the United States, the forming andmachining of mica insulators is relatively costly, and the quality ofmica insulators is not always satisfactory.

Mica being a natural mineral and containing a varying amount ofchemically combined water of crystallization in its composition, tendsto decompose when heated giving up its water of crystallization anddeteriorating in crystalline form to that of an anhydrous powder, andthus deteriorates rapidly from its initial characteristics when used asa spark plug insulator in a high compression engine.

With the development of higher compression motors, mica becomesincreasingly unsatisfactory as an insulator for the spark plugs for themotors, and other substances have been used including ordinary porcelainand mullite porcelain.

Ordinary porcelain, such as a composition of feldspar, pure clay, andflint fired to a temperature of 2300 to 2500 F., constitutes a superiorform of burned clay product, but for spark plug insulator use hasrelatively poor resistance to the thermal shock imposed upon the sparkplug insulators of a high compression motor.

Furthermore ordinary porcelain has a low dielectric strength,particularly when hot, and is in fact an electrical conductor when hot.Ordinary porcelain also has insufficient thermal conduc- 1 Claim. (Cl.106-66) tivity for use as a satisfactory aircraft engine spark pluginsulator, and furthermore is subject to attack by the lead compoundspresent in the combustion gases of high octane tetra ethyl leadgasolines.

Mullite porcelains, composed chiefly of clay and silica minerals, suchas sillimanite, fired together at a temperature of approximately 2700Ft, develop into strong crystalline structures having improvedmechanical strength and improved hot dielectric strength as compared toordinary porcelains, but still lacking sufficient thermal conductivityand chemical stabliity necessary for use as spark plug insulators inhigh compression aircraft motors.

It has been determined to be desirable for use as spark plug insulatorsin high compression aircraft motors to provide a fired composition ofmatter having the greatest attainable combination of the followingproperties:

1. Vitreousness to a high degree and extremely low porosity; l

2. Hot dielectric strength in excess of megohms at 1000 F.;

3. Resistance to thermal shock so as not to be subject to fracture whenquenched in water at room temperature from a temperature of 400 F.;

4. Mechanical strength greater than 100,000 lbs. per sq. in. incompression;

5. Thermal expansion of 7.00 X 10";

6. High thermal conductivity;

7. Hardness and resistance to wear such that the hardness is 9 or overon Mohs scale;

8. Inert with common acids at normal temperatures,.that is not subjectto appreciable loss in hot or cold HCl, H2804, HNOa, or H3PO4;

9. Resistant to corrosion in molten lead oxide;

10. Absorptive of radiant energy.

Pure aluminum oxide has been found to attain a combination of the aboveproperties satisfactory for use in the vitrified state as insulators foraircraft engine spark plugs.

The commercial production of vitrified articles from pure aluminumoxide, or alumina, has not been found practicablebecause of theextremely high temperatures required to bring about the condensation ofa pure alumina body to the point of complete vitreousness free fromporosity, and because the lack of plasticity of pure alumina renders itsformation as a body into any particular shape such as that of aninsulator very diflicult.

By the present discovery and invention, it has been found that thepresence of a very small amount of substantially any other inorganic submina will be about in the same degree.

3 stance in a body otherwise including substantially all alumina willproduce a pronounced depression in the temperature necessary for thevitrifiti n of he b dy Q mpOsition,,and wiliim rove the formingadaptability. f I I It has further been discovered that'a combination ofa relatively great variety of other substances to a total of a verysmall amount in a body, the remainder of whichis substantially. allalumina, has a more pronouncedefiect in depressing the vitrificationtemperature than when only one or two other substances with alumina areused for the body.

It has further been discovered that by using a combination of four ormore other substances with alumina in the body, that the total amount ofthe added substances can be kept very low in proportion to the aluminaand thatin this way the properties of the body and the firedyproduct arepredominately those of alumina, and stability is attainedin theproduction of the firedproducts without the sacrifice of any,substantial amount of the desired properties ofthe majoringredientalumina.

Plotting the effects of the various added substances on a phase rulediagram reveals a leveling off of the effects through the combination ofthe various added ingredients, so that instead of sharp changesaffecting the combination, the changes are more gradual and the firingrange of the combination is greatly extended and stabilized.

Furthermore, the addition of a relatively great variety of substances tothe predominant alumina provides a factor of safety against thevariations that normally exist in the commercial forms of thesubstances, so that a more stable and dependable body is obtainedthrough the use in the body composition of a wide variety of substancesadded to the alumina.

Also it has been discovered that regardless of the specified substanceadded to the alumina, if added in minute amount, the effect on the alu-The alumina in the resultant mixture or body is overwhelmingly thepredominant material, and the resultant body has substantially theproperties of that of pure alumina.

In attaining a combination of the highest degree of the-above enumeratedproperties for a fired composition of matter for use as aircraft enginespark plug insulators, it has been found preferably to use bodycombinations of aluminum oxide with the addition of chromium oxide in aminor quantity plus :theaddition of small quantities vof other inorganicsubstances preferably the oxides of the other metals.

In particular the chromium oxide produces in the fired article a strongpink-or rose color at room temperature. Without the chromium oxide thefired articles'are white in color. The strong pink or rose colorproduced in the fired article by the chromium oxide changes when hot, aswhen the article is in useas an insulator in an aircraft engine sparkplug, to black which imparts to the insulator the property of greaterheat absorption bythe absorption Ofradiant heat from the gases ofcombustion in the engine cylinder, the radiant heat being otherwisereflected by white or coated bodies;

To the predominant alumina, the chromium oxide is added and smallquantities of other substances selected from a wide variety of metallic:oxides and compounds.

The"; total amount of the added" substances m ef abiy,-not.exceeds8z%zzof:th ztotarcom- $1.5 avoiding :silica contamination in theprocessing,

4 position, the remaining 92% being alumina. It is preferable that thetotal number of added substances be more than three.

All the added substances areselectedfrom the following metals in theiroxide or other; compound forms:

Aluminum Mercury Antimony Molybdenum Arsenic Nickel Barium OsmiumBeryllium Platinum Bismuth Potassium Boron Praseodymium Cadmium RubidiumCaesium Scandium Calcium Selenium Cerium Silicon Chromium Silver CobaltSodium Columbium Strontium Copper Tantalum Dysprosium Thallium GalliumThorium Germanium Tin Gold Titanium Indium Tungsten Iridium TelluriumIron Uranium Lanthanum Vanadium Lead Yttrium Lithium Zinc MagnesiumZirconium Manganese The above metals are included in groups .1, 2, 3,

4, 5, 6, 7, 8 of the periodic table of elements of matter.

While it has been found that the presence of the alkalis of group 1 ofthe periodic table of elements, particularly sodium and potassium, aredeleterious to the fired composition in causing a reduction in hotdielectric strength, it is a Practical impossibility to avoid traces tomeasurable amounts of these substances in the body.

Furthermore, it has been found that a proportion of these alkalis not inexcess of 0.05% does not sufficiently deteriorate the bodydielectrically to cause any seriously harmful results, and that theirpresence in combination with other substances, particularly the alkalineearths of group 2 of the periodic table of elements andboron, developsl'oW .fusion combinations and intensifies the fiuxing action of themass. Therefore allowance for the presence of these alkaline substancesis made .in the particular body compositions of the present discoveryand invention.

Thealumina in'the body composition or mixture should be in excess of 92%and preferably in excess of 95%. It has been found impractical fromafiring standpoint to vitrify mixtures much in excess of 95% aluminajHowever the properties of the product are much improved as the aluminais increased, and laboratory products have been .made at temperatures of3400 F. in

.65 which compositions as high as 98% of alumina were vitrified,yielding an excellent. product, but impractical to produce in commercialpractice at present because of the exceedingly high temperaturerequired.

The alumina is preferably in excess of 99% A1203 and as stated freeiromalkalis. in excess of 0.05% and also free from silica in excess of Thesilica content of the bodyis, minimized by and by using silicates aslittle as possible in the body composition. Where calcium, magnesium,chromium, beryllium, and barium are used in the body composition, theforms of these substances may be in the compounds including fluorides,carbonates, oxides, phosphates, sulphates, etc., to avoid the silicates.All the added substances should be preferably in the dehydrated form,and free from the alkalis, lithium, sodium, and potassium.

However, by the introduction of fluorides into the body composition,silicates of the metals, such as magnesium in the form of talc may beused to a limited extent without harmful results from subsequent silicacontamination, because the fluorine set free by the reaction resultingfrom the firing of the body composition combines with the silica to formgaseous silicon tetra fluoride which escapes and constitutes avolatilization of the silicon.

Describing one particular composition of matter or body composition I ofthe discovery and invention and the method of making the same, theprincipal ingredient of the body composition is calcined aluminum oxide,which before use in the compounding of the body is highly refined andfreed of soluble impurities by lixiviation after being ground to asub-microscopic grain size.

To 92 parts by Weight of this purified and finely ground alumina A1203is added and thoroughly mixed 1%; parts of calcium fluoride CaFz and 1parts magnesium phosphate Mg3(PO4)2.4H2O, 4 parts of plastic ball clayA12O3.2S1O2.2H2O and 1 part of chromic oxide CrzOs.

In the grinding of the alumina to sub-microscopic grain size, quartzstones are generally used as grinding media, and in the grinding theabrasiveness of the calcined alumina on the quartz grinding stonescauses about 1 /2 to 2% of silica vto be ground into the alumina so thatthe alumina after grinding has a composition of 98 to 98/ A1203 and 1 t2% SiOz.

In the preferred manner of grinding the alumina for the bodies of thepresent invention, a rubber lines mill is used, and the grinding ballsare formed of fired alumina, thereby avoiding the pick-up of silica inthe ground alumina.

It has further been discovered that the initial .calcination of thefluxing ingredients alone or in combination with part or all of thealumina is desirable before the final body is formed and the finalfiring effected.

Eutectics are formed between alumina and a combination of various othersubstances. However the formation of these eutectics requires initiallya very high temperature, at which point the firing range of the mixtureis very short due to the sudden depression of the melting point at thetemperature of the formation of the eutectics.

When however the mixture is fused or calcined and then ground andre-formed, as the final body composition, upon the second heating, thesintering point is reached at a much lower temperature because of thepreviously formed eutectics.

A combination of many ingredients yields a superior result than whenonly few are used, since the eutectics formed between alumina and a widevariety of substances in combination provides a wide range oftemperature over which the various eutectics are active, whereas With alesser number, the range is correspondingly shorter.

The above described body composition I after the second firing to atemperature of over 3000 F., produces a fired product consistingofaluminum in excess of 92%, and the oxides of the added metals,silicon, calcium, chromium, and magnesium, the fired product havingdesired properties as set forth herein for use as an aircraft spark pluginsulator, and other purposes.

Examples of other body compositions, made according to the presentdiscovery and invention, and processed as set forth herein to producethe improved fired product including alumina and other metallic oxides,are as follows:

Body composition II Percent Alumina, aluminum oxide 92.25 Talc,magnesium silicate 1.25 Fluorspar, calcium fluoride 2.00 Clay, aluminumsilicate 3.50 Chromium oxide 1.00

100.00 Body composition III Percent Alumina, aluminum oxide 91.68 Talc,magnesium silicate 1.25 Whiting, calcium carbonate 2.57 Clay, aluminumsilicate 3.50 Chromium oxide 1.00

100.00 Body composition IV Percent Alumina, aluminum oxide 92.04 Talc,magnesium silicate 1.25 Barium carbonate 0.89 Whiting, calcium carbonate0.44 Clay, aluminum silicate 3.50 Chromium oxide 1.00 Beryllium silicate0.88

The embodiments of the compositions of matter and the method steps ofmaking the same described herein are by way of example, and the scop ofthe present discovery and invention is not limited to the same or to theparticular details thereof, but is commensurate with any and all novelsubject matter contained herein which may at any time properly under theUnited States patent laws be set forth in the claim hereof ororiginating herein, and the elements of any such claim are intended toinclude their reasonable equivalents.

I claim:

A body composition of matter, for a fired vitreous product, includingthe following compounds, mixed in parts by weight:

Alumina, aluminum oxide 91.68

HAROLD R. FEICHTER.

